The Loops 07 site has been gradually adding mp3 files for the plenary and parallel talks, the most recent additon was 13 July. Here are some plenary talks that have audios---which I've listened to while scrolling thru the slides.(adsbygoogle = window.adsbygoogle || []).push({});

http://www.matmor.unam.mx/eventos/loops07/

In this first batch, I had some idea already what to expect from the talks by Ashtekar, Rovelli, and Thiemann. So although the talks were clear, organized, informative, I was not bowled over. On the other hand I want to say YOU HAVE TO WATCH the talks by ORITI, REUTER, and RIDEOUT. For me, they had a surprise factor that made them extra impressive.

Oriti has important new results in Group Field Theory (background independent field including gravity translated to live on a cartesian product of groups).

Reuter is a highly credible contrarian, or so I found.

Rideout and co-workers apply supercomputers to quantum gravity (see also supercomputing reports in parallel sessions by Christensen, Cherrington, Khavkine)

Plenary talks

Abhay Ashtekar:LQG: Lessons from models· slides (pdf) · audio (mp3)

In the last couple of years, several simple but physically interesting models were solved. Solutions led to concrete and detailed realizations of a number of ideas that have been heuristically expected for decades. There were also some surprises. These analyses suggest viewpoints and strategies for full quantum gravity. I will summarize some of them in broad terms.

Daniele Oriti:Group field theory: spacetime from quantum discreteness to an emergent continuum· slides (pdf) · audio (mp3)

Group field theories are non-local quantum field theories on group manifolds, and a generalization of matrix models. Having been first introduced in the context of simplicial quantum gravity, have gained attention as being potentially of much interest in the context of loop quantum gravity and spin foam models. After a brief introduction to the group field theory formalism, I review some of the results already obtained in this approach. I will then try to offer a new perspective on how group field theories should be interpreted and used towards a complete theory of quantum gravity. In particular, I will argue that group field theories can represent on the one hand a common unifying framework for loop quantum gravity, spin foam models and simplicial approaches, like quantum Regge calculus and dynamical triangulations, and on the other hand a consistent microscopic description of spacetime considered as a condensed matter system. From this, a novel approach to the issues of the emergence of the continuum and of General Relativity as an effective description of spacetime, in this approximation, is proposed. Finally, I will briefly report on some recent results and work in progress inspired by and supporting this new perspective.

Martin Reuter:Asymptotically safe quantum gravity and cosmology· slides (pdf) · audio (mp3)

The basic ideas and main results of the asymptotic safety scenario in Quantum Einstein Gravity (QEG) are reviewed and possible implications for the cosmology of the early universe are discussed.

David Rideout:Can the supercomputer provide new insights into quantum gravity?· slides (pdf) · audio (mp3)

Machine computation is a relatively unutilized tool in quantum gravity, in part because of the enormous scale of the problems which arise, and the corresponding substantial initial investment which must be made to write code for supercomputers. However, the advent of computational frameworks, such as Cactus, is changing this situation, by drastically decreasing the time required to develop code for supercomputers. I will briefly describe the Cactus framework, and present three insights that have arisen from its use. One is with regard to how entropy bounds may arise from discrete gravity, a second regarding how continuum topology may emerge from an underlying causal set, and third how the nature of the spectrum of the Ashtekar-Lewandowski volume operator of Loop Quantum Gravity depends crucially on the nature of the embedding of a spin network vertex.

Carlo Rovelli:The LQG vertex· slides (pdf) · slides (key.zip) · audio (mp3)

It has recently been possible to begin the computation of n-points functions in loop quantum gravity. I review the basic ideas and the present state of these calculations. The Barrett-Crane vertex appears to yield some n-point functions with the correct low-energy limit, but there are also indications of a wrong behavior. The problem can be traced to the way intertwiner quantum numbers are treated in the Barrett-Crane model. This is also the source of the general discrepancy between the Barrett-Crane vertex and LQG. I present a new vertex for loop quantum gravity, introduced in collaboration with Jonathan Engle and Roberto Pereira, which may correct the problem and is fully consistent with the LQG kinematics.

Thomas Thiemann:Loop Quantum Gravity (LQG): From secured land to unknown territory· slides (pdf) · audio (mp3)

We describe the conceptual and mathematical setup of Loop Quantum Gravity (LQG).

Last modified 13 July 2007.

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Here are some talks for which slides, but not yet audio files, are available---or for which we don't yet have slides---or which I simply haven't yet had time to take in.

Jan Ambjørn:4d quantum gravity as a sum over histories· audio (mp3)

In this plenary talk I will review the attempts to formulate 4d quantum gravity as a sum over histories in such a way that computer simulations can be performed. I will report on computer simulations of a quantum universe with a positive cosmological constant as well as a quantum universe where test matter is included.

Martin Bojowald:Loop quantum gravity and effective theory· slides (pdf)

Several models have been defined to study the broad framework of loop quantum gravity. We present a common perspective for cosmology where configurations are close to being isotropic. Effective techniques are then used to illustrate important features of the semiclassical limit and to show examples of correction terms to Einstein's equation. Applications include corrections to the Newton potential and to cosmological perturbation equations relevant for the CMB power spectrum.

Sabine Hossenfelder:Phenomenological Quantum Gravity· slides (pdf)

The search for a satisfying theory that unifies general relativity with quantum field theory is surely one of the major tasks for physicists in the 21st century. During the last decade, the phenomenology of quantum gravity and string theory has been examined from various points of view, opening new perspectives and testable predictions. I will give a short introduction into these effective models which allow to extend the standard model and include the expected effects of the underlying fundamental theory. I will talk about models with extra dimensions, models with a minimal length scale and those with a deformation of Lorentz invariance. The focus is on observable consequences, such as black hole and graviton production and modifications of standard-model cross-sections.

Fotini Markopoulou:Quantum gravity and emergent locality· slides (pdf)

An important aspect of the desired low energy limit of a background independent quantum theory of gravity is to show how locality arises in the emergent low energy theory. We discuss why we should not expect the high energy theory to have our geometric notions of locality. We present two models of a high energy breakdown of locality: a disordered locality perturbation of a flat geometry and a fully pre-geometric system with no notion of locality which has a local ground state.

Alejandro Perez:Regulator dependence in quantum gravity and non perturbative renormalizability: possible new perspectives· slides (pdf) · audio (mp3)

Topological field theories are simple examples of background independent field theories which are non perturbatively renormalizable in the sense that regularization ambiguities have no effect on physical quantities. Three dimensional vacuum general relativity coupled to point particles is an important example of such theory. The corresponding generalization to higher dimensions has been studied recently. In four dimensions, one-dimensional extended objects (strings) are the natural form of matter that couples to four dimensional BF theory. After briefly reviewing these models, we will show how these topological theories of extended objects can accommodate physically interesting degrees of freedom maintaining their topological nature. We will propose a way by which topological theories of 2d world-sheet matter (of the kind presented in the first part of the talk) might be used to construct background independent quantum field theories with local degrees of freedom and no regulator dependence.

Lee Smolin:Chiral excitations of quantum geometry as elementary particles· slides (pdf) · slides (ppt)

Rafael Sorkin:Quantum reality and anhomomorphic logic· audio (mp3)

Histories-based forms of quantum mechanics seem better suited to the needs of quantum gravity than the more familiar alternative based on state-vectors and selfadjoint operators. Such a re-casting of the theory opens up the possibility to dispense with "external observers" by introducing the concept of an "event" and locating the predictive content of the formalism in the "preclusion" of certain events. The most straightforward such preclusion rule engenders contradictions which are fatal if one sticks with classical logic, but which can be accommodated by an "anhomomorphic logic" that effectively identifies reality with a Z_2 valued function on the space of possible events.

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# Which Morelia audios are available?

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